The present invention generally relates to a method for dehydrating porous materials, such as moist walls and/or floors of a masonry or concrete structure, as well as the clay containment structure of a landfill, through the use of electro-osmosis. More particularly, the present invention relates to applying a D.C. voltage of a specific pulse pattern to an anode embedded in a porous material, and allowing the voltage to travel through the porous material to a cathode embedded in earth.
Moisture problems in containment structures are common, particularly in building structures located at least partially underground. In addition, modem day efforts to minimize building erection time often do not allow adequate drying time for concrete, leading to moisture problems in the building structure. number of these methods require significant energy and time to achieve the marginal results.
The principle of electro-osmosis was discovered by Professor F. F. Reuss in Moscow in 1807. Electro-osmosis employs a voltage potential difference between two points on opposite sides of a porous material. If the porous structure of the material has been saturated by water, the porous materials assume a negative potential. This causes positive ions in the water to locate around the porous materials to form a so-called electrical double layer. The positive ions will move towards a region having a lower voltage potential. The positive ions are hydrated, and therefore each ion carries a small amount of water, resulting in a water flow toward the lower potential.
There have been a number of commercial attempts to dehydrate building structures using electro-osmosis. In some European countries, a so-called xe2x80x9cpassivexe2x80x9d electro-osmosis system has been employed, wherein a natural potential difference which is created between a moist material and its surroundings is used. This type of installation has yielded marginal results.
In other types of electro-osmosis systems, a direct current or conventional alternating current has been used to generate a potential difference. With these systems, it is only possible to carry water between the anode and cathode over a short period of time, because the forces after some period will reverse such that the electrolyte (water) is transported back to its origin. Efforts were thus directed toward developing a system capable of functioning over an extended period of time, without the so-called xe2x80x9czeta potentialxe2x80x9d being reversed, meaning that the water returns back to the capillary material. A number of system have been developed utilizing a pulsating direct current, that is where the current is switched between positive and negative potentials. Such systems are described in U.S. Pat. Nos. 5,368,709; 4,600,486; and 5,015,351; as well as in Swedish patent applications 8106785-2 and 8601888-4 (P. Eliassen), Swedish Patent No. 450264 and Polish Patent No. 140265 (Basinsky et al.). These known systems have problems relating to the durability of the electrodes on the anode side of the system because the anodes are easily corroded due to a reduction-oxidation phenomenon. In addition, these known systems have not balanced the energy of the positive and negative pulses in voltage-seconds, also denoted as magnetic flux, so that a maximum water flow out of porous material of the structure is obtained without having a further moisturizing of the porous material at a later time.
It is an object of the invention to provide a novel method and apparatus for dehydrating porous materials which sustains the transport of liquid in the desired direction.
It is a further object of the invention to provide an improved electro-osmotic method and apparatus for dehydrating porous materials which reduces the drying time and lowers the relative humidity compared to known methods.
It is yet another object of the present invention to provide a novel electro-osmotic method and apparatus for dehydrating porous materials to a lower relative humidity level than prior art methods and apparatus.
The above and other objects are accomplished according to the invention by the provision of a method and apparatus for dehydrating a porous material using electro-osmosis, including the steps of: applying a pattern of D.C. voltage pulses to an anode system embedded in the material, the anode system being electrically interactive with a cathode structure embedded in earth, wherein the pattern of D.C. voltage pulses has a pulse period T in a range from about 3 to about 60 seconds, and each pulse period includes a positive pulse duration T+ from about 0.7T to about 0.97T, a negative pulse duration Txe2x88x92 from about 0.01T to about 0.05T and a neutral pulse duration Tp from about 0.02T to about 0.25T.
It has been found that by utilizing a pulse pattern according to one preferred embodiment of the invention, an osmotic pressure differential from one side to the other of a structure made of porous material can be sustained which is at least ten times greater than that possible with known electro-osmotic techniques.
In accordance with another preferred embodiment of the invention, each pulse period includes two or more positive pulses separated by at least one of either a negative pulse or a neutral pulse, with the positive pulse duration T+ being the combined duration of the two positive pulses, an even greater osmotic pressure differential is developed.
Other objects, features and advantages of the invention will become apparent from the following detailed description of the invention when taken in conjunction with the accompanying drawings.